Watching cells in action

09 November 2007

Chemists in Canada are using scanning electrochemical microscopy to image cells and at the same time follow their metabolic activity.

Zhifeng Ding and Piotr Diakowski of the University of Western Ontario in London modified commercially-available atomic force microscopy (AFM) equipment to perform alternating current scanning electrochemical microscopy (AC-SECM). This method uses a microelectrode as a probe for measuring the current in close proximity to the cell, recording it as a function of the tip position.

"SECM provides electrochemical information as well as topographic information"

'Unlike AFM,' Ding explained, 'which provides only topographic information, SECM also carries electrochemical information.' The major advantage of the alternating current SECM arises from the fact that no additional redox species is needed - 'especially important when the presence of toxic species is not desired in a biological system,' said Ding.

The duo's set-up allows AC-SECM images to be obtained in a relatively short time period, which is particularly important for unstable biological specimens. Also, although AC-SECM offers lower resolution than AFM, it does not alter the cell topography. AFM images of living cells often show sharp spikes due to the soft cell membrane being swept along in the scan direction by the AFM tip. This problem does not arise with AC-SECM since the method does not require direct contact between the tip and the sample.

Alternating current scanning electrochemical microscopy can be used to image cells without altering their topography

The researchers were also able to use the method to follow metabolic activity at the cell surface. The current's dependence on tip-to-sample separation distance allowed them to monitor contractions in the cell following the addition of ethanol, a cytotoxin. Also, by fixing the position of the scanning tip and chemically-inducing a burst of cellular respiration, Ding and Diakowski could qualitatively detect the cell's metabolic activity as an increase in reactive oxygen species production.

Ding said that 'while this system has the potential to be applied in the investigation of any soft samples that are difficult to image using AFM, we are going to use it for monitoring metabolic activities of living cells and tissues without use of any markers. We intend to observe simultaneous changes in shape and metabolism by means of AC-SECM combined with conventional SECM. These developments and applications toward chemical imaging of the biological systems will be further pursued in our laboratory.'